The general objective of the PI's research is to understand events in olfactory processing that lead to the discrimination of odorant mixtures. In humans and animals, the perceived intensity or quality of individual odorant compounds is changed when they are mixed; these events are called mixture interactions. this implies that there are interactions between pathways activated by odorants and that these interactions can influence the response to the mixture. In this proposal, experiments are presented that will test the idea that the identity of a mixture is derived by the peripheral and central olfactory system from the unique set of neurons activated by that mixture, and that the composition of the unique set of activated neurons depends on the nature of excitatory and inhibitory pathways activated by the components and on the interactions between these pathways. The spiny lobster will be used as the animal model in these studies, since it possesses many of the basic design features of the mammalian olfactory system, including a glomerularly organized olfactory neuropil, and it is a well studied model system. Coding of mixtures by single olfactory receptor neurons and interneurons will be examined using electrophysiological techniques. Activity of ensembles of cells will be examined with activity dependent labeling techniques. The structure of receptor molecules and their genes will be explored using biochemical and molecular approaches.